The present invention relates to a seed drill for applying seed and/or fertilizer, wherein the sowing shares are attached to a frame in such a way that they can move in an upright plane by means of superimposed and at least approximately parallel struts on parallelogram mounts.
A seed drill of this type is known from German OS No. 3 216 376 corresponding in part to U.S. Pat. No. 4,580,507. The sowing shares therein are positioned on the frame by means of parallelogram mounts. The practical result is that the shares always assume the same orientation with respect to the surface of the soil. Since the drill is mostly employed on uncultivated soils, the shares must penetrate into a hard soil that has stones and other obstacles distributed through it to some extent, cutting a furrow in the soil that seed and fertilizers if necessary are then deposited in. One problem in this type of approach, which is called direct sowing and includes the zero, minimum, and reduced tillage methods, is that the stones and other obstacles are entrenched very stubbornly in the uncultivated soil and cannot be shifted to the side by the sowing shares when encountered by them.
To enable the shares to avoid such stones or other obstacles, a system called stone counteraction is built into the parallelogram mounts on this drill. The upper struts in the mounts are designed to yield against a resilient force, allowing each share to swing back and slide over the stone or other obstacle.
Although this type of stone counteraction has been proven in practice, it has turned out to be not always completely satisfactory. Stone security, the capacity, that is, of the upper struts on the parallelogram mount to yield and allow the shares to pivot out of the way, works adequately only when the share encounters an obstacle more or less frontally. When, however, the share encounters a surface of the obstacle that is oriented at an angle to the direction of travel, the share is forced to one side and will not swing back because the resulting force component is too weak to make the strut yield. Forcing the share to the side will bend the share mount or the share itself.